This was a collaborative project with the BPL in which the human research was conducted on the Residential Research Unit and parallel animal studies were conducted in the BPL. The use of the self-administration (SA) study paradigm permitted an assessment of the relative contribution of environmental and pharmacologic factors to the self-administration of drugs. Parallel comparative studies in squirrel monkeys and humans in which subjects are given the opportunity to self-administer comparable doses of cocaine and nicotine under similar behavioral schedules and experimental conditions also provide a means to assess the generality of biological variables influencing drug SA. This research has shown that responding is maintained in human subjects. The stimuli that are associated with injections of cocaine develop conditioned reinforcing effects in the humans in a manner similar to the manner in which these effects develop in squirrel monkeys. These studies have also demonstrated that a research strategy employing drug SA in human subjects can yield all of the important information of single-dose studies, and also, provide information on the direct reinforcing effects of the compound which may be compared to the large base of animal drug SA. Data collection has been completed and need only to undergo final analyses before publication.